1. Field of the Invention
The present invention relates to a high-density magnetic recording and reproducing head for recording high-density information on and reproducing high-density information from a magnetic recording medium.
2. Description of the Prior Art
There have been developed magnetic recording mediums with high coercive forces to meet demands for high-density magnetic recording of desired information. Perpendicular magnetic recording has been proposed which employs a magnetic recording medium with perpendicular magnetic anisotropy.
Thin-film magnetic recording and reproducing heads have been developed for achieving narrower recording tracks and shorter wavelengths. The tendency in the field of magnetic recording and reproducing heads is being shifted from bulk heads toward thin-film heads.
Another developing effort has been directed to a thin-film magnetic head based on the magnetoresistive (MR) effect that is dedicated for reproducing recorded signals. The thin-film magnetic head does not depend on the relative speed between the magnetic head itself and a magnetic recording medium, the relative speed being lower as the density of recorded signals is higher. The MR magnetic head has an MR magnetic sensing section composed of a thin film of Permalloy. There has not been developed a material having a large MR effect, i.e., a sufficiently large ratio .DELTA.R/R of a resistance change .DELTA.R caused when a magnetic field is applied to a resistance R when no magnetic field is applied. The ratio .DELTA.R/R of the Permalloy is of a small value of 2%.
Recently, there has been proposed an active magnetic head which utilizes a change in the inductance of a coil under an external magnetic field (see, for example, the lecture preprint No. 5, page 35, for the spring national convention of Electronic Information Communication Society, 1990).
The applicant has proposed a microwave waveguide type magnetic detecting device capable of reproducing, with high sensitivity, a signal magnetic field produced by a signal magnetically recorded on a magnetic recording medium, as disclosed in Japanese patent application No. 3-333687.
As shown in FIG. 1 of the accompanying drawings, the disclosed magnetic detecting device is embodied as a magnetic reproducing head comprising a microwave waveguide 2 positioned at a terminal end thereof and including a soft magnetic material 1 whose magnetic permeability varies due to an external magnetic field applied, and a high-frequency oscillator 3 for oscillating the microwave waveguide 2.
A magnetic field to be detected, i.e., a signal magnetic field produced by a signal magnetically recorded on a magnetic recording medium 4, is applied to the soft magnetic material 1. The magnetic permeability of the soft magnetic material 1 varies when the applied magnetic field varies. When the magnetic permeability of the soft magnetic material 1 varies, the impedance of the microwave waveguide 2 varies, resulting in a change in the reflectivity of the high-frequency electric energy supplied to the microwave waveguide 2. The change in the reflectivity of the supplied high-frequency electric energy results in a voltage change at a certain location in the microwave waveguide 2, which is measured as the change in the applied external field.
The principle of operation of the microwave waveguide type magnetic reproducing head will further be described below. When a microwave waveguide which is not matched at a load end thereof is oscillated by high-frequency electric energy supplied through a microwave transmission line such as a coaxial cable, a reflected wave as well as a traveling wave exist in the waveguide, producing a standing wave resulting from the overlapping reflected and traveling waves. The amplitude ratio of the standing wave is maximum in those microwave waveguides whose load end is open or short-circuited.
FIG. 2 of the accompanying drawings shows the magnitude .vertline.V.vertline. of a standing wave in the microwave waveguide 2 whose load end is open. The solid-line curve shown in FIG. 2 indicates that a standing wave exists whose amplitude .vertline.V.vertline. is minimum at x=x.sub.0. In FIG. 2, the ratio of the maximum amplitude to the minimum amplitude of the standing wave is referred to as a voltage standing wave ratio, and .lambda. indicates a distance or pitch between adjacent two of repetitive cycles of the standing wave.
The voltage standing wave ratio and the pitch .lambda. depend on the magnetic permeability B in the waveguide. When the magnetic permeability .mu. varies with the external magnetic field Hex, the voltage standing wave ratio and the pitch .lambda. also vary, resulting in a change in the standing wave as indicated by the broken-line curve in FIG. 2. According to the broken-line curve, the standing wave amplitude .vertline.V.vertline. becomes a voltage Vex at x=x.sub.0. Therefore, the external magnetic field Hex can be detected based on the voltage Vex.
The microwave waveguide 2 may be in form of a microwave stripline. The microwave stripline comprises, as shown in FIG. 1, a grounded conductor 5 and a line conductor 6, with a dielectric 7 and the soft magnetic material interposed therebetween.
The soft magnetic material 1 has its magnetic permeability B depending sharply on the applied magnetic field. When the magnetic field is applied in a certain direction, the magnetic permeability of the soft magnetic material 1 increases. As the applied magnetic field increases in intensity, the the magnetic permeability of the soft magnetic material 1 decreases.
The microwave stripline has its load end 2a open. At the other end of the microwave waveguide 2 remote from the load end 2a, the high-frequency oscillator 3 is connected between the grounded conductor 5 and the line conductor 6 through a transmission line 8 which may comprise a coaxial cable.
The microwave waveguide 2 is oscillated by the high-frequency oscillator 3 with a frequency of about 1 GHz, for example, with no signal magnetic field applied. The frequency of the high-frequency oscillator 3 is adjusted so that the standing wave amplitude is minimum at x=x.sub.0, as indicated by the solid-line curve in FIG. 2. At x=x.sub.0, the standing wave voltage is detected by a detecting circuit 9, and measured by a voltmeter 10.
As shown in FIG. 1, the open load end 2a of the microwave waveguide 2 is positioned closely to the magnetic recording medium 4 in confronting relationship thereto. A leakage magnetic field, i.e., a signal magnetic field, produced by a signal magnetically recorded on the magnetic recording medium 4 is applied as an external magnetic field Hex to the soft magnetic material 1. Since the magnetic permeability .mu. of the soft magnetic material 1 changes due to the applied external magnetic field Hex, the voltage standing wave and the standing wave pitch .lambda. also vary as indicated by the broken-line curve in FIG. 2. Therefore, the magnetically recorded signal can be read as the voltage change.
When the frequency of the high-frequency oscillator 3, i.e., the carrier frequency f, is selected to be of 1 GHz, for example, even if the signal magnetic field Hex is of a sufficiently high frequency of about 100 MHz, the carrier can be removed by the detecting circuit 9, and only the change in the signal magnetic field Hex can be detected as the voltage change.
The microwave waveguide type magnetic reproducing head can be fabricated by the thin film technology.
However, there is a limitation on the track width of any thin film magnetic heads because of problems in the fabricating process and magnetic characteristics. Consequently, it is necessary to record signals in shorter wavelengths for higher recording density.
Since the MR magnetic head and microwave waveguide type magnetic head, referred to above, are dedicated for reproducing recorded signals, some fabrication problems such as their positioning and structural complexities arise out of combining themselves with recording heads.